In a present communications system, communication is generally performed in an FDD (Frequency Division Duplex) manner or a TDD (Time Division Duplex) manner. In an FDD system, uplink and downlink communication is performed by means of different frequencies. In a mobile communications system in a TDD mode, receiving and transmission are performed in different timeslots on a same frequency channel (that is, carrier), and timeslots are used to differentiate a receive channel from a transmit channel. In both communication manners, for a signal, communication can be performed only within a period of time or in a specific frequency band.
A full-duplex wireless communications technology is a technology different from TDD and FDD. Co-time co-frequency communication can be implemented by using the technology. However, when two communications devices perform co-time co-frequency communication, a receive antenna not only receives a desired signal from a peer end, but also receives a signal transmitted by the receive antenna itself, that is, a self-interference signal. In addition, because a distance between a transmit antenna and the receive antenna is extremely close, strength of the self-interference signal is usually much higher than that of the desired signal from the peer end.
Currently, the following method is generally used to cancel the self-interference signal: a digital signal is obtained through coupling from a digital domain for transmission, the self-interference signal is then reconstructed, and finally, the self-interference signal is canceled in a digital domain for receiving. However, the method cannot cancel a phase noise, non-linearity, and a noise floor that are introduced at a transmit end, and therefore has poor self-interference cancellation performance.